1. Field of the Invention
The present invention relates to a magnetic recording disk cartridge provided with a rigid casing encasing therein a rotatable flexible magnetic recording disk having a spiral track or concentric circular tracks formed thereon in which information is written and read by a recording and retrieving head through a head window formed at a predetermined position of the casing. More particularly, the present invention relates to a magnetic recording disk cartridge provided with a casing able to encase therein a metallic thin film type magnetic disk having, e.g., a thin Co system alloy film with a high magnetic recording density, and enables a high speed access, a high durability, and a high reliability.
2. Description of the Related Art
In the magnetic recording disk cartridge accommodating therein a magnetic recording disk having a high magnetic recording density, fine dust and fingerprints on and damage mechanically applied to the surface of the magnetic recording disk adversely affect the recording performance of the magnetic recording disk, and therefore, the magnetic recording disk is encased in a portable casing to cover the magnetic recording disk. The recording and retrieving of information is carried out by a magnetic recording and retrieving head through a head window provided at a predetermined position of the casing of the magnetic recording disk cartridge.
Japanese Unexamined Patent Publication No. 57-212669 discloses an improved magnetic recording disk cartridge provided with a closing member or a shutter to close a head window of the cartridge, to prevent dust and fingerprints impinging on the magnetic recording disk surface through the head window, as well as to protect the magnetic recording disk surface from being damaged via the head window. The cartridge of the Japanese Unexamined Patent Publication No. 57-212669 is constructed in such a manner that the head window is opened only when the magnetic recording disk cartridge is set in a magnetic recording disk drive unit, and is automatically closed by the shutter when the magnetic recording disk cartridge is taken out of the drive unit. The improved magnetic recording disk cartridge of the Japanese Unexamined Patent Publication No. 57-212669 enhances the reliability of a safe storage of a magnetic recording disk and a safe insertion of the magnetic recording disk cartridge into a magnetic recording disk drive unit, and therefore, when the improved construction of the Japanese Unexamined Patent Publication No. 57-212669 is applied to a magnetic recording disk cartridge incorporating therein a coating type flexible magnetic recording disk coated with a magnetic recording medium, such as a .gamma.- Fe2 03, the cartridge can be used without the occurrence of any particular technical problem.
On the other hand, Japanese Unexamined Patent Publications No. 52-134706 and No. 53-3209 disclose a thin film type magnetic recording medium employing a magnetic thin film capable of exhibiting a high recording density which cannot be expected by the abovementioned coating type magnetic recording medium, to satisfy a requirement for increasing the density of recording and retrieving information. These Publications No. 52-134706 and No. 53-3209 also discloses a perpendicular magnetic recording and retrieving mechanism by which a high speed accessibility and highly precise recording are realized and a retrieving mechanism used with the above-mentioned thin film type magnetic recording medium.
Nevertheless, when a conventional cartridge casing for the conventional coated type magnetic recording disk is directly used for encasing the abovementioned thin film type flexible magnetic recording disk having on the face thereof a magnetic recording medium made of a strong magnetic metal film or a metallic oxide film, it has been found that a serious defect arises from the viewpoint of the performance of a magnetic recording disk cartridge. Namely, a nonwoven cloth liner of the conventional cartridge casing arranged to be in sliding contact with the face of the coating type magnetic recording disk, to thereby promote a smooth and stable rotation of the coated type magnetic recording disk and prevent dust on the recording face or the observe face of the disk, cannot properly exhibit these functions with the respect to the afore-mentioned thin film type flexible magnetic recording disk. This is because, as the face of the thin film type flexible magnetic recording disk is generally covered with a protective layer made of a metallic oxide layer or a thin carbon layer, the face becomes harder than that of the conventional coating type flexible magnetic recording disk, and as a result, when the above-mentioned nonwoven-cloth liner of the conventional cartridge casing is arranged to be in sliding contact with the face of the thin film type flexible magnetic recording disk, the liner is abraded to generate a collection of abraded fine materials intervening between the face of the magnetic recording disk and a magnetic recording and retrieving head when the cartridge is used with the magnetic disk drive unit. Therefore, either the face of the flexible magnetic recording disk and the end face of the magnetic recording and retrieving head are damaged or a small spacing appears between the face of the flexible magnetic recording disk and the end face of the magnetic recording and retrieving head to prevent an appropriate magnetic recording and retrieving operation, and thus a reliable recording and retrieving operation cannot be obtained from the combination of the thin film type magnetic recording disk and the conventional cartridge casing with the nonwoven cloth liner. In addition, it has been found that, even if a fine adjustment of the sliding contact between the nonwoven cloth liner and the thin film type flexible magnetic recording disk is made, a rotating torque detected during the rotation of the disk is greatly different among different thin film type flexible magnetic recording disks, and therefore, it is difficult to realize a reliable magnetic disk drive system when the conventional nonwoven cloth liner is used for a cartridge of the thin film type flexible magnetic recording disk.
Japanese Unexamined Patent Publication No. 62-33385, to the present inventors at al., discloses a novel casing for a magnetic recording disk cartridge capable of overcoming the above-mentioned difficulty. The casing of the cartridge disclosed in the Japanese Unexamined Patent Publication No. 62-33385 has a plurality of hard projections made of a sliding material, to replace the conventional nonwoven cloth liner. The hard projections of the casing are arranged to confront a peripheral portion of each face of the magnetic recording disk encased in the casing and are circumferentially spaced apart from one another. It was confirmed that the operational life of the magnetic recording disk cartridge with the hard projections has been prolonged while overcoming the above-mentioned difficulty. But, during subsequent research and experiments by the present inventors, it was found that sometimes disturbances appear in the wave form of the retrieving signal retrieved by a magnetic retrieving head from the thin film type magnetic recording disk, and accordingly, errors in the retrieving of information from the magnetic recording disk occur. Therefore, the present inventors conducted further investigations to detect the cause of the above-mentioned errors. At this stage, it should be appreciated that, since the flexible magnetic recording disk must be rotated in the casing of the cartridge without fluctuating with respect to a flat plane, to achieve a stable recording and retrieving of information on the face of the thin film type flexible magnetic recording disk, when the magnetic recording disk cartridge is rotated by a disk drive unit about a rotating axis of the cartridge, fluctuation of the face of the magnetic recording disk is suppressed to less than a predetermined value by reducing a distance between the ends of the hard projections and the face of the flexible magnetic recording disk. Nevertheless, it was found that the above-mentioned small distance left between the ends of the hard projections and the face of the flexible magnetic recording disk causes the aforementioned retrieving errors.